Interference cancellation system

ABSTRACT

Embodiments of the inventive concepts disclosed herein are directed to a system for cancelling interference. The system may include a first antenna and a second antenna spatially separated from the first antenna. The system may include a first time delay unit, coupled to the first antenna, and configured to apply a first time delay and first power gain on a first signal received by the first antenna. The system may include a control circuit, coupled to the first time delay unit, and configured to determine the first time delay and first power gain to cause a modified version of the first signal and a second signal, received by the second antenna, to be aligned in time and power levels.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a divisional of U.S. application Ser. No.16/130,344, filed Sep. 13, 2018, which is hereby incorporated byreference herein in its entirety.

GOVERNMENT LICENSE RIGHTS

This invention was made with government support underDOTC-16-01/W15QKN-14-9-1001 and DOTC-16-01-INIT0266-RC-01 awarded by theDepartment of Defense Ordnance Technology Consortium. The government hascertain rights in the invention.

BACKGROUND

Radio frequency (RF) communication systems can be utilized in variousenvironments. Interferences may occur in such RF systems and mayinterrupt, obstruct, or otherwise degrade or limit the effectiveperformance of the communication. Various interferences can occur in anRF communication system such as, for example, co-site interferences,self-interferences, self-network interferences, and intentionalinterferences (or sometimes referred to as jammer interferences).

SUMMARY

In one aspect, embodiments of the inventive concepts disclosed hereinare directed to a system for cancelling interference. The system mayinclude a first antenna and a second antenna spatially separated fromthe first antenna. The system may include a first time delay unit,coupled to the first antenna, and configured to apply a first time delayand first power gain on a first signal received by the first antenna.The system may include a control circuit, coupled to the first timedelay unit, and configured to determine the first time delay and firstpower gain to cause a modified version of the first signal and a secondsignal, received by the second antenna, to be aligned in time and powerlevels.

In another aspect, embodiments of the inventive concepts disclosedherein are directed to a system for automatically cancellinginterference. The system may include a first antenna and a secondantenna spatially separated from the first antenna. The system mayinclude a first time delay unit configured to apply a first time delayand first power gain on a first signal received by the first antenna toprovide a modified version of the first signal. The system may include asecond time delay unit configured to apply a second time delay andsecond power gain on a second signal received by the second antenna toprovide a modified version of the second signal. The system may includea first subtractor configured to subtract respective power levels of themodified version of the first signal and the modified version of thesecond signal to provide a first output signal. The system may include afirst control circuit configured to determine the first and second timedelays and first and second power gains based on a power level of thefirst output signal to cause the modified version of the first signaland the modified version of the second signal to be aligned in time andpower levels.

In yet another aspect, embodiments of the inventive concepts disclosedherein are directed to a system for automatically cancellinginterference. The system may include a first antenna and a secondantenna spatially separated from the first antenna. The system mayinclude a first time delay unit configured to apply a first time delayand first power gain on a first signal received by the first antenna toprovide a first modified version of the first signal. The system mayinclude a second time delay unit configured to apply a second time delayand second power gain on a second signal received by the second antennato provide a first modified version of the second signal. The system mayinclude a third time delay unit configured to apply a third time delayand third power gain on the first signal received by the first antennato provide a second modified version of the first signal. The system mayinclude a fourth time delay unit configured to apply a fourth time delayand fourth power gain on the second signal received by the secondantenna to provide a second modified version of the second signal. Thesystem may include a first subtractor configured to subtract respectivepower levels of the first modified version of the first signal and thefirst modified version of the second signal to provide a first outputsignal. The system may include a first control circuit configured todetermine the first and second time delays and first and second powergains based on a power level of the first output signal to cause thefirst modified version of the first signal and the first modifiedversion of the second signal to be aligned in time and power levels. Thesystem may include a second subtractor configured to subtract respectivepower levels of the second modified version of the first signal and thesecond modified version of the second signal to provide a second outputsignal. The system may include a second control circuit configured todetermine the third and fourth time delays and third and fourth powergains based on a power level of the second output signal to cause thesecond modified version of the first signal and the second modifiedversion of the second signal to be aligned in time and power levels.

BRIEF DESCRIPTION OF THE DRAWINGS

Implementations of the inventive concepts disclosed herein may be betterunderstood when consideration is given to the following detaileddescription thereof. Such description makes reference to the includeddrawings, which are not necessarily to scale, and in which some featuresmay be exaggerated and some features may be omitted or may berepresented schematically in the interest of clarity. Like referencenumerals in the drawings may represent and refer to the same or similarelement, feature, or function. In the drawings:

FIG. 1A is a block diagram of an RF communication system, in accordancewith some embodiments of the inventive concepts disclosed herein;

FIG. 1B is a block diagram of an RF communication system, in accordancewith some embodiments of the inventive concepts disclosed herein;

FIG. 1C is a block diagram of an RF communication system, in accordancewith some embodiments of the inventive concepts disclosed herein;

FIG. 1D is a block diagram of a mutual coupling mitigation circuit ofthe RF communication system of FIG. 1C, in accordance with someembodiments of the inventive concepts disclosed herein.

FIG. 2 shows a block diagram of an RF communication system, inaccordance with some embodiments of the inventive concepts disclosedherein;

FIG. 3 shows a block diagram of an RF communication system, inaccordance with some embodiments of the inventive concepts disclosedherein;

FIG. 4 shows a block diagram of an RF communication system, inaccordance with some embodiments of the inventive concepts disclosedherein;

FIGS. 5A and 5B collectively show a block diagram of an RF communicationsystem, in accordance with some embodiments of the inventive conceptsdisclosed herein;

FIG. 6 shows a flow chart of an exemplary method to operate the RFcommunication systems of FIGS. 1A-D, in accordance with some embodimentsof the inventive concepts disclosed herein;

FIG. 7 shows a flow chart of an exemplary method to operate the RFcommunication systems of FIG. 2, in accordance with some embodiments ofthe inventive concepts disclosed herein;

FIG. 8 shows a flow chart of an exemplary method to operate the RFcommunication systems of FIG. 3, in accordance with some embodiments ofthe inventive concepts disclosed herein;

FIG. 9A shows a symbolic diagram of nulls, in accordance with someembodiments of the inventive concepts disclosed herein;

FIG. 9B shows an antenna polar plot corresponding to the symbolicdiagram of FIG. 9A, in accordance with some embodiments of the inventiveconcepts disclosed herein;

FIG. 10 shows various symbolic diagrams and corresponding antenna polarplots of nulls and/or aliased nulls, in accordance with some embodimentsof the inventive concepts disclosed herein; and

FIGS. 11A and 11B show symbolic diagrams of overlapped andnon-overlapped nulls, respectively, in accordance with some embodimentsof the inventive concepts disclosed herein

DETAILED DESCRIPTION

Before describing in detail embodiments of the inventive conceptsdisclosed herein, it should be observed that the inventive conceptsdisclosed herein include, but are not limited to a novel structuralcombination of components and circuits, and not to the particulardetailed configurations thereof. Accordingly, the structure, methods,functions, control and arrangement of components and circuits have, forthe most part, been illustrated in the drawings by readilyunderstandable block representations and schematic diagrams, in ordernot to obscure the disclosure with structural details which will bereadily apparent to those skilled in the art, having the benefit of thedescription herein. Further, the inventive concepts disclosed herein arenot limited to the particular embodiments depicted in the schematicdiagrams, but should be construed in accordance with the language in theclaims.

The present disclosure provides various embodiments of systems andmethods to cancel the above-mentioned interferences. In someembodiments, an RF communication system and a method to operate the sameare disclosed. The RF communication system can include a pair ofantennas. At least a first one of the pair of antennas can be coupled bya time delay unit that can apply dynamically configurable, adjustable,or determined time delays and power gains on a signal received by thefirst antenna. A second one of the pair of antennas can be coupled by nosuch a time delay, another time delay unit that can also applydynamically configurable, adjustable, or determined time delays andpower gains on a signal received by the second antenna, or yet anothertime delay unit that can apply a fixed time delay and power gain on thesignal received by the second antenna. In some embodiments, thedynamically configurable, adjustable, or determined time delays andpower gains, respectively applied on the signals received by first andsecond antennas, can be determined by a control circuit throughmonitoring or measuring whether such modified (e.g., delayed in time andamplified in power) signals can be aligned in time and power levels. Inresponse to determining that the two modified signals are aligned intime and power levels, the RF communication system can provide one ormore nulls against an interference based on the time delays and powergains respectively applied on the signals received by the first andsecond antennas.

For purposes of reading the description of the various embodimentsbelow, the following descriptions of the sections of the specificationand their respective contents may be helpful:

Section A describes various embodiments of an RF communication system.

Section B describes exemplary methods to respectively operate the RFcommunication systems described in Section A.

Section C describes nulls and/or aliased nulls generated by the RFcommunications systems described in Section A.

A. RF Communication System

Referring to FIG. 1A, depicted is a functional block diagram of an RFcommunication system 100. As shown in FIG. 1A, the RF communicationsystem 100 includes a first antenna 102, a second antenna 104, a firsttime delay unit (TDU) 106, a second TDU 106, a combiner 110, a controlcircuit 112, and an RF front end 114. The components 102-114 shown inthe illustrated embodiment of FIG. 1A may constitute a portion of the RFcommunication system 100, which can further include any of various otherRF communication components such as, for example, one or more digitalbaseband processing subsystems, one or more digital-to-analog processingsubsystems, one or more transmitting subsystems, etc., while remainingwithin the scope of the present disclosure. Such subsystems shall bediscussed with respect to FIGS. 5A-B.

In some embodiments, the TDU 106 can be coupled to the antenna 102, andthe TDU 108 can be coupled to the antenna 104. The antennas 102 and 104,physically separated apart from each other by a distance 115, canreceive one or more RF signals e.g., signal 116. Depending on thedirections along which the antennas 102 and 104 receive the one or moreRF signals 116, signals 118 and 120 respectively received through or bythe antennas 102 and 104 (sometimes respectively referred to as“received signal 118” and “received signal 120”) can be different, e.g.,presenting a phase difference therebetween. Such a phase difference maybe associated with a propagation delay between the antennas 102 and 104.The TDU 106 can apply dynamically configurable, adjustable, ordetermined time delays and power gains on the received signal 118 toprovide a modified version of the received signals 118 (sometimesrespectively referred to as “modified signal 122”); and the TDU 108 canapply dynamically configurable, adjustable, or determined time delaysand power gains on the received signal 120 to provide a modified versionof the received signals 120 (sometimes respectively referred to as“modified signal 122”).

Each of the TDUs 106 and 108 can include one or more components to applythe time delay and power gain on the received signal. In someembodiments, the TDU can include one or more true time delay (TTD)devices/units, at least one of which can provide an adjustable, avariable, or programmable time delay, and one or more amplifiers orattenuators, at least one of which can provide an adjustable, avariable, or programmable power gain, or gain. As shall be discussedbelow, respective values of such adjustable time delays and power gainsmay be determined by the control circuit 112.

The combiner 110 is coupled to the TDUs 106 and 108 to receive themodified signals 122 and 124. In some embodiments, the combiner 110 canbe a 180° hybrid combiner, which can perform a subtraction function onthe modified signals 122 and 124. In response to receiving the modifiedsignals 122 and 124, the combiner 110 can perform a subtraction functionon the modified signals 122 and 124 to provide an output signal 126 tothe control circuit 112 and RF front end 114. In the case where themodified signals 122 and 124 are aligned in time and power levels (bythe TDUs 106 and 108, respectively), the combiner 110 can provide theoutput signal 126 as one or more nulls, which may be used to minimize oreliminate interferences that can be included within the one or more RFsignals 116. Such a null shall be discussed in further detail below withrespect to FIGS. 9A-B.

The control circuit 112 can use the output signal 126, received from thecombiner 110, to determine the time delay and power gain that the TDU106 applies on the received signal 118, and provide the determined timedelay and power gain to the TDU 106. Similarly, the control circuit 112can use the output signal 126, received from the combiner 110, todetermine the time delay and power gain that the TDU 108 applies on thereceived signal 118, and provide the determined time delay and powergain to the TDU 108.

In some embodiments, the control circuit 112 can determine a power levelof the output signal 126, and based on the power level of the outputsignal 126 to determine the time delays and power gains respectivelyused by the TDUs 106 and 108. For example, the control circuit 112 caniteratively update the time delays and/or power gains that the TDUs 106and 108 respectively use on the received signals 106 and 108 based onthe power level of the output signal 126. In some embodiments, thecontrol circuit 112 can determine the respective time delays and powergains respectively used by the TDUs 106 and 108 to cause the combiner110 to provide the output signal 126 as one or more nulls, responsive todetermining that the corresponding power level of the output signal 126is a minimum over plural iterations of updating the time delays and/orpower gains (used by the TDUs 106 and 108, respectively). Such a nullshall be discussed in further detail below with respect to FIGS. 9A-B.

The RF front end 114 can process the output signal 126 to generate oneor more digital signals to be further processed by one or more othersubsystems of the RF communication system 100. In some embodiments, theRF front end 114 can include one or more components to collectivelyperform at least a function to convert the output signal from an analogdomain to a digital domain. As such, the RF front end 114 can bereferred to as an analog-to-digital portion, or RF-to-baseband portion,of the RF communication system 100. For example, the RF front end 114can include one or more filters, one or more detectors, one or moreamplifiers, one or more local oscillators, one or more analog-to-digitalconverters, etc., which shall be discussed with respect to FIGS. 5A-B.

In some embodiments, the control circuit 112 can automatically performthe above-discussed iterations, which is sometimes referred to as anauto-nulling function or nulling function, until at least a null isdetermined (e.g., a direction of the null is determined). Such a nullingfunction can be selectively enabled by the RF communication system 100based on various criteria such as, for example, responsive to the RFcommunication system 100 determining that the power consumption of theRF front end 114 has exceeded a predefined threshold. By enabling thenulling function, the RF communication system 100 can minimize oreliminate one or more interferences received by the RF communicationsystem 100, even though sources, locations, and/or directions of suchinterferences are unknown. In some other embodiments, the RFcommunication system 100 can calibrate the TDUs 106 and 108 todetermine, log, or manage the respective directions of one or more nullsthat the RF communication system 100 may provide. As such, if thedirection of an interference is known, the RF communication system 100can readily use the calibrated settings of TDUs 106 and 108 to eliminateor minimize the known interference.

Referring to FIG. 1B, depicted is a functional block diagram of an RFcommunication system 130. As shown in FIG. 1B, the RF communicationsystem 130 includes a first antenna 132, a second antenna 134, a timedelay unit (TDU) 136, a combiner 138, a control circuit 140, and an RFfront end 142. The components 132-142 shown in the illustratedembodiment of FIG. 1B may constitute a portion of the RF communicationsystem 130, which can further include any of various other RFcommunication components such as, for example, one or more digitalbaseband processing subsystems, one or more digital-to-analog processingsubsystems, one or more transmitting subsystems, etc., while remainingwithin the scope of the present disclosure. Such other subsystems shallbe discussed with respect to FIGS. 5A-B.

The RF communication system 130 is substantially similar as the RFcommunication system 100 of FIG. 1A except that in the RF communicationsystem 130, only one of the antennas 132 and 134 is coupled with a TDU.Accordingly, the similar components (e.g., 136-142) may be brieflydiscussed below.

In the illustrated embodiment of FIG. 1B, the antennas 132 and 134,physically separated apart from each other by a distance 135, canreceive one or more RF signals e.g., signal 146. Depending on thedirections along which the antennas 132 and 134 receive the one or moreRF signals 146, signals 148 and 150 respectively received through or bythe antennas 132 and 134 (sometimes respectively referred to as“received signal 148” and “received signal 150”) can be different, e.g.,presenting a phase difference therebetween.

In some embodiments, the antenna 132 may be directly coupled to thecombiner 138, and the antenna 134 may be coupled to the combiner via theTDU 136. The TDU 136 can apply dynamically configurable, adjustable, ordetermined time delays and power gains on the received signal 150 togenerate a modified signal 152 (e.g., delayed in time by the time delayand amplified in power by the power gain), while the received signal 148may not be delayed in time or amplified in power. The combiner 138(e.g., a subtractor) can receive the received signal 148 and modifiedsignal 152 as inputs and perform a subtraction function on the signals148 and 152 to provide an output signal 154. The control circuit 140 andRF front end 142 can receive the output signal 154 as respective inputs.

Similar as the control circuit 112 of FIG. 1A, the control circuit 140can determine a power level of the output signal 154, and based on thepower level of the output signal 154 to determine the time delay andpower gain used by the TDU 136. In some embodiments, the control circuit140 can iteratively update the time delays and/or power gains that theTDU 136 uses on the received signals 150 based on the power level of theoutput signal 154. In some embodiments, the control circuit 140 candetermine the time delay and power gain used by the TDU 136 to cause thecombiner 138 to provide the output signal 154 as one or more nulls,responsive to determining a minimum power level of the output signal 154over a number of iterations. In other words, the received signal 148,without being delayed and amplified, and the modified signal 152, withbeing delayed by the time delay and amplified by the power gaindetermined by the control circuit 140 in response to determining thatthe corresponding power level of the output signal 154 is a minimum overplural iterations of updating the time delays and/or power gains (usedby the TDU 136). Such a null may be used to minimize or eliminateinterferences that can be included within the one or more RF signals146. The null, which shall be discussed in further detail below withrespect to FIGS. 9A-B, can be provided to the RF front end 142 forfurther processing. The RF front end 142 is substantially similar to theRF front end 114 of FIG. 1A so that the discussions are not repeated.

The combiner 138 may receive the signal 148, without being delayed bydynamically adjustable time delays and amplified by dynamicallyadjustable power gains, as one of the inputs, as discussed above. Insome other embodiments, the combiner 138 may receive the signal 148,which can be delayed in time by a predefined or fixed amount of timedelay and amplified in power by a predefined or fixed amount of powergain. The fixed amount of time delay may be greater than the maximumvalue of a propagation delay between the antennas 132 and 134. Such apredefined amount of time delay and predefined amount of power gain maybe applied on the signal 148 by one or more components such as, forexample, a transmission line, a phase shifter, an amplifier, etc.

Referring to FIG. 1C, depicted is a functional block diagram of an RFcommunication system 160. As shown in FIG. 1C, the RF communicationsystem 160 includes a first antenna 162, a second antenna 164, a mutualcoupling (MC) mitigation circuit 166, a first time delay unit (TDU) 168,a second TDU 170, a combiner 172, a control circuit 174, and an RF frontend 176. The components 162-176 shown in the illustrated embodiment ofFIG. 1C may constitute a portion of the RF communication system 160,which can further include any of various other RF communicationcomponents such as, for example, one or more digital baseband processingsubsystems, one or more digital-to-analog processing subsystems, one ormore transmitting subsystems, etc., while remaining within the scope ofthe present disclosure. Such subsystems shall be discussed with respectto FIGS. 5A-B.

The RF communication system 160 is substantially similar as the RFcommunication system 100 of FIG. 1A except that the RF communicationsystem 160 can further include an MC mitigation circuit (e.g., 166).Accordingly, the similar components (e.g., 168-174) may be brieflydiscussed below.

In the illustrated embodiment of FIG. 1C, the antennas 162 and 164,physically separated apart from each other by a distance 177, canreceive one or more RF signals e.g., signal 178. Depending on thedirections along which the antennas 162 and 164 receive the one or moreRF signals 178, signals 180 and 182 respectively received through or bythe antennas 162 and 164 (sometimes respectively referred to as“received signal 162” and “received signal 164”) can be different, e.g.,presenting a phase difference therebetween. In some instances, when theantennas 162 and 164 receive the RF signal 178, at least one of theantennas 162 and 164 may re-radiate, backscatter, or scatter the RFsignal 178, which can cause a mutual coupling between the antennas 162and 164. Such a mutual coupling effect may be present in one or both ofthe received signals 180 and 182.

In some embodiments, the MC mitigation circuit 166, coupled to theantennas 162 and 164, can mitigate, minimize, or eliminate the mutualcoupling effect present in one or both of the received signals 180 and182 by measuring a power level of a signal re-radiated or scattered fromone of the antennas 162 and 164 and, if needed, compensating the signalreceived by the other of the antennas 162 and 164. FIG. 1D illustratesan example of an embodiment of the MC mitigation circuit 166. As shown,the MC mitigation circuit 166 can include branches 1 and 2, each ofwhich can include a splitter, a delay circuit (e.g., a true time delay(TTD)), an attenuation circuit (ATTN), and a subtractor. For example,branch 1 can include a splitter 193-1, a TTD 195-1, an ATTN 196-1, and asubtractor 197-1; and branch 2 can include a splitter 193-2, a TTD195-2, an ATTN 196-2, and a subtractor 197-2. The splitter 193-1 ofbranch 1 can route the received signal 180 to the subtractor 197-1 ofthe same branch and to the TTD 195-2 and ATTN 196-2 of branch 2.Similarly, the splitter 193-2 of branch 2 can route the received signal182 to the subtractor 197-2 of the same branch and to the TTD 195-1 andATTN 196-1 of branch 1. As such, a first signal containing the mutualcoupling effect, received by one of the antennas, can be mitigated bysubtracting a second signal, received by the other of the antennas andthen adjusted by the TTD and ATTN, from the first signal. In response tomitigating the mutual coupling effect, the MC mitigation circuit 166 canprovide signals 184 and 186 to the TUDs 168 and 170, respectively. Thesignals 184 and 186 may be sometimes referred to as “mitigated signal184” and “mitigated signal 186,” respectively.

In response to receiving the mitigated signals 184 and 186, the TDU 168can apply dynamically configurable, adjustable, or determined timedelays and power gains on the mitigated signal 184 to generate amodified signal 188 (e.g., delayed in time by the time delay andamplified in power by the power gain); and the TDU 170 can applydynamically configurable, adjustable, or determined time delays andpower gains on the mitigated signal 186 to generate a modified signal190 (e.g., delayed in time by the time delay and amplified in power bythe power gain). Similarly, such modified signals 188 and 190 can becombined by the combiner 172 to generate an output signal 192. Thecontrol circuit 174 can receive the output signal 192 to determine therespective time delays and power gains that the TDUs 168 and 170 use.The combiner 174 can generate the output signal 192 as one or more nullsto eliminate or minimize interferences that can be included in RF signal178. The RF front end 176 can receive the output signal 192 to furtherprocess the signal 192. Since the RF front end 176 can be substantiallysimilar to the above-discussed RF front end, the discussions as to theRF front end 176 are not repeated.

In some other embodiments, the RF communication system 160 mayoptionally include one of the TDUs 168 and 170. The RF communicationsystem 160 can be substantially similar to the RF communication system130 except for including the MC mitigation circuit 166. In suchembodiments, one of the mitigated signals 184 or 186 may be delayed intime by a dynamically configurable, adjustable, or determined time delayand/or amplified in power by a dynamically configurable, adjustable, ordetermined power gain, while the other of the mitigated signals 184 or186 may or may not be delayed in time by a fixed time delay and/oramplified in power by a fixed power gain.

The above-discussed RF communication systems 100, 130, and 160 may beused to receive an RF signal with a single band, in accordance with someembodiments of the present disclosure. Embodiments of the RFcommunication systems of the present disclosure, however, are notlimited to being used in a single band environment. According to someembodiments, the RF communication systems 200, 300, and 400,respectively illustrated in FIGS. 2, 3, and 4, can each be used in amulti-band environment. For example, each of the RF communicationsystems 200, 300, and 400 can receive a number of RF signals, which canreside in respective different bands, and provide one or more nulls ateach of the different bands.

Referring to FIG. 2, a functional block diagram of the RF communicationsystem 200 is depicted. As shown in FIG. 2, the RF communication system200 can include a first antenna portion 210, a second antenna portion230, a combiner 250, and an RF front end 252. Each of the antennaportions 210 and 230 may include one or more components, which shall bediscussed below. The components shown in the illustrated embodiment ofFIG. 2 may constitute a portion of the RF communication system 200,which can further include any of various other RF communicationcomponents such as, for example, one or more digital baseband processingsubsystems, one or more digital-to-analog processing subsystems, one ormore transmitting subsystems, etc., while remaining within the scope ofthe present disclosure. Such other subsystems shall be discussed withrespect to FIGS. 5A-B.

In some embodiments, the first antenna portion 210 may provide one ormore nulls at a first band; and the second antenna portion 230 mayprovide one or more nulls at a second band, wherein the second band isdifferent from the first band. Although two antenna portions are shownin the illustrated embodiment of FIG. 2, the RF communication system 200can include any desired number of antenna portions while remainingwithin the scope of the present disclosure. As such, the RFcommunication system 200 can provide nulls at respective different bandsthat are more than 2.

The antenna portion 210 can include a first antenna 212, a secondantenna 214, a first filter 216, a second filter 218, a first time delayunit (TDU) 220, a second TDU 222, a control circuit 224, and a combiner226. The antennas 212 and 214 may be physically apart from each other bya distance 227. Similarly, the antenna portion 230 can include a firstantenna 232, a second antenna 234, a first filter 236, a second filter238, a first TDU 240, a second TDU 242, a control circuit 244, and acombiner 246. The antennas 232 and 234 may be physically apart from eachother by a distance 247. The antenna portions 210 and 230 can be eachsubstantially similar as a portion of the RF communication system 100(e.g., 102-110 of FIG. 1A) except that the antenna portions 210 and 230can each include a pair of filters coupled between respective antennasand TDUs. Thus, the discussions of similar components are repeatedagain.

In the antenna portion 210, the filter 216 can be coupled between theantenna 212 and TDU 220; and the filter 218 can be coupled between theantenna 214 and TDU 222. In some embodiments, each of the filters 216and 218 can include a band-pass filter that can allow the portion of asignal within a certain frequency range to pass therethrough and reject,or attenuate, the portion of the signal outside the frequency range.Such a frequency range used by the filters 216 and 218 may correspond toa first band (hereinafter “band 1”) in which the antenna portion 210generates nulls.

For example, the RF communication system 200 can receive one or more RFsignals 254 with a frequency ranging from about 2 GHz to 6 GHz. Inresponse to the antenna portion 210 receiving the RF signal 254, thefilters 216 and 218 may filter received signals 256 and 258,respectively received through or by the antennas 212 and 214. The filter216 may pass the portion of the signal 256 inside band 1 (e.g., about2˜3 GHz) and reject the portion of the signal 256 outside band 1. Thefilter 218 may pass the portion of the signal 258 inside band 1 (e.g.,about 2˜3 GHz) and reject the portion of the signal 258 outside band 1.As such, in response to receiving such filtered signals 260 and 262, theTDUs 220 and 222, control circuit 224, and combiner 226 of the antennaportion 210 can follow the similar operations, as discussed above, togenerate an output signal 264 as one or more nulls at band 1.

Similarly, in the antenna portion 230, the filter 236 can be coupledbetween the antenna 232 and TDU 240; and the filter 238 can be coupledbetween the antenna 234 and TDU 242. In some embodiments, the filters236 and 238 of the antenna portion 230 may use another differentfrequency range (e.g., about 3˜4 GHz), which may correspond to a secondband (hereinafter “band 2”), to filter the respective signals receivedthrough or by the antennas 232 and 234. Accordingly, the TDUs 240 and242, control circuit 244, and combiner 246 of the antenna portion 230can follow the similar operations, as discussed above, to generate anoutput signal 266 as one or more nulls at band 2.

In some embodiments, the combiner 250 can combine the respective outputsignals generated by the antenna portions, e.g., 210 and 230, andprovide a single combined signal 268 to the RF front end 252 for furtherprocessing, as discussed above. Continuing with the above example, thecombiner 250 can combine (e.g., add) the output signals 264 and 266,each of which can include one or more nulls at the respective band, andprovide such the signal 268 to the RF front end 252 for furtherprocessing.

Referring to FIG. 3, a functional block diagram of the RF communicationsystem 300 is depicted. As shown in FIG. 3, the RF communication system300 can include a first antenna 302, a second antenna 304, a firstsplitter 306, a second splitter 308, a first nulling portion 310, asecond nulling portion 330, a combiner 344, and an RF front end 346.Each of the nulling portions 310 and 330 may include one or morecomponents, which shall be discussed below. The components shown in theillustrated embodiment of FIG. 3 may constitute a portion of the RFcommunication system 300, which can further include any of various otherRF communication components such as, for example, one or more digitalbaseband processing subsystems, one or more digital-to-analog processingsubsystems, one or more transmitting subsystems, etc., while remainingwithin the scope of the present disclosure. Such other subsystems shallbe discussed with respect to FIGS. 5A-B.

The antennas 302 and 304 of the RF communication system 300 may bephysically apart from each other by a distance 303. The RF communicationsystem 300 can receive one or more RF signals 350 using the antennas 302and 304. In response to receiving the RF signals 350, the splitters 306and 308, respectively coupled to the antennas 302 and 304, can eachsplit, divide, or route the respective received signal into a number ofrouted signals to respective nulling portions, according to someembodiments. Each of such a number of routed signals may have an equalamplitude, 0° phase difference between one and anther, and/or an equalpower level. For example, the splitter 306 can split received signal 352(the signal 350 received by the antenna 302) into routed signals 352-1,352-2, etc.; and the splitter 308 can split signal 354 (the signal 350received by the antenna 304) into routed signals 354-1, 354-2, etc. Therouted signals 352-1 and 354-1 can be provided to the first nullingportion 310; and the routed signals 352-2 and 354-2 can be provided tothe nulling portion 330.

In some embodiments, the first nulling portion 310 may provide one ormore nulls at a first band; and the second nulling portion 330 mayprovide one or more nulls at a second band, wherein the second band isdifferent from the first band. Although two nulling portions are shownin the illustrated embodiment of FIG. 3, the RF communication system 300can include any desired number of nulling portions while remainingwithin the scope of the present disclosure. As such, the RFcommunication system 300 can provide nulls at respective different bandsthat are more than 2.

The nulling portion 310 can include a first filer 312, a second filter314, a first time delay unit (TDU) 316, a second TDU 318, a controlcircuit 320, and a combiner 322. The nulling portion 330 can include afirst filer 332, a second filter 334, a first TDU 336, a second TDU 338,a control circuit 340, and a combiner 342. In some embodiments, each ofthe nulling portions 310 and 330 of the RF communication system 300 canbe substantially similar to the antenna portion of the RF communicationsystem 200 (e.g., 210 and 230) except that the nulling portions may notinclude an antenna, and each of the TDUs of the nulling portion mayreceive a routed signal (e.g., 352-1, 354-1, etc.) as input. Thus, thenulling portions 310 and 330 of the RF communication system 300 may bebriefly discussed below.

According to some embodiments, each of the filters 312, 314, 332, and334 can include a band-pass filter that can allow the portion of asignal within a certain frequency range to pass therethrough and reject,or attenuate, the portion of the signal outside the frequency range. Thefrequency range used by the filters 312 and 314 of the first nullingportion 310 may correspond to a first band (hereinafter “band 1”) inwhich the nulling portion 310 generates nulls; and the frequency rangeused by the filters 312 and 314 of the second nulling portion 330 maycorrespond to a second band (hereinafter “band 2”) in which the nullingportion 330 generates nulls.

For example, the RF communication system 300 can receive one or more RFsignals 350 with a frequency ranging from about 2 GHz to 6 GHz. Inresponse to the antenna 302 and 304 receiving the RF signal 350 as thereceived signals 352 and 354, respectively, the splitter 306, coupled tothe antenna 302, can split the received signal 352 into routed signals352-1 and 352-2; and the splitter 308, coupled to the antenna 304, cansplit the received signal 354 into routed signals 354-1 and 354-2. Eachof the routed signals 352-1-2 and 354-1-2 may remain to have thefrequency, as received (e.g., substantially similar as the respectivereceived signal), according to some embodiments. Each of the respectivedifferent nulling portions 310 and 330 can receive a number of routedsignals respectively split from different splitters.

In response, the filters 312 and 314 of the nulling portion 310 mayfilter routed signals 352-1 and 354-1, respectively. The filter 312 maypass the portion of the signal 352-1 inside band 1 (e.g., about 2˜3 GHz)and reject the portion of the signal 352-1 outside band 1. The filter314 may pass the portion of the signal 354-1 inside band 1 (e.g., about2˜3 GHz) and reject the portion of the signal 354-1 outside band 1.Similar as the operation discussed above with respect to the antennaportions 210 and 230 of FIG. 2, responsive to receiving the signalsfiltered by the filters 312 and 314, the TDUs 316 and 318, controlcircuit 320, and combiner 322 can generate an output signal 356 as oneor more nulls at band 1.

Similarly, in response to receiving the routed signals 352-2 and 354-2,the filters 332 and 334 of the nulling portion 330 may filter routedsignals 352-2 and 354-2, respectively. The filter 332 may pass theportion of the signal 352-2 inside band 2 (e.g., about 3˜4 GHz) andreject the portion of the signal 352-2 outside band 2. The filter 334may pass the portion of the signal 354-2 inside band 2 (e.g., about 3˜4GHz) and reject the portion of the signal 354-2 outside band 2. Andresponsive to receiving the signals filtered by the filters 332 and 334,the TDUs 336 and 338, control circuit 340, and combiner 342 can generatean output signal 358 as one or more nulls at band 2.

In some embodiments, the combiner 344 can combine the respective outputsignals generated by the nulling portions, e.g., 310 and 330, andprovide a single combined signal 360 to the RF front end 346 for furtherprocessing, as discussed above. Continuing with the above example, thecombiner 344 can combine (e.g., add) the output signals 356 and 358,each of which can include one or more nulls at the respective band, andprovide the signal 360 to the RF front end 346 for further processing.

Referring to FIG. 4, a functional block diagram of the RF communicationsystem 400 is depicted. As shown in FIG. 4, the RF communication system400 can include a first antenna array portion 402, a second antennaarray portion 452, a first beamforming circuit 454, a second beamformingcircuit 456, a combiner 458, and an RF front end 460. Each of theantenna array portions 402 and 452 may include one or more components,which shall be discussed below. The components shown in the illustratedembodiment of FIG. 4 may constitute a portion of the RF communicationsystem 400, which can further include any of various other RFcommunication components such as, for example, one or more digitalbaseband processing subsystems, one or more digital-to-analog processingsubsystems, one or more transmitting subsystems, etc., while remainingwithin the scope of the present disclosure. Such other subsystems shallbe discussed with respect to FIGS. 5A-B.

In some embodiments, each of the antenna array portions (e.g., 402 and452) of the RF communication system 400 can be substantially similar asa combination of the pair of antennas 302 and 304, the pair of splitters306 and 308, and the plural nulling portions 310 and 330 of FIG. 3.Therefore, the antenna array portions of the RF communication system 400may be briefly described as follows.

As shown in the illustrated embodiment of FIG. 4, the first antennaarray portion 402 can include a first antenna 404, a second antenna 406physically separated from the first antenna 404 by a distance 405, afirst splitter 408, a second splitter 410, a first nulling portion 411,and a second nulling portion 431. Similar as the nulling portionsdiscussed with respect to FIG. 3, the first nulling portion 411 caninclude filters (e.g., band-pass filters) 412 and 414, TDUs 416 and 418,a control circuit 420, and a combiner (e.g., a subtractor) 422; and thesecond nulling portion 431 can include filters (e.g., band-pass filters)432 and 434, TDUs 436 and 438, a control circuit 440, and a combiner(e.g., a subtractor) 442. The first nulling portion 411 can provide anoutput signal 423 as one or more nulls at a first band (hereinafter“band 1”); and the second nulling portion 431 can provide an outputsignal 445 as one or more nulls at a second band (hereinafter “band 2”),wherein the second band is different from the first band.

Similarly, the second antenna array portion 452 can include a firstantenna 454, a second antenna 456 physically separated from the firstantenna 454 by a distance 455, a first splitter 458, a second splitter460, a first nulling portion 461, and a second nulling portion 481.Similar as the nulling portions discussed with respect to FIG. 3, thefirst nulling portion 461 can include filters (e.g., band-pass filters)462 and 464, TDUs 466 and 468, a control circuit 470, and a combiner(e.g., a subtractor) 472; and the second nulling portion 481 can includefilters (e.g., band-pass filters) 482 and 484, TDUs 486 and 488, acontrol circuit 490, and a combiner (e.g., a subtractor) 492. The firstnulling portion 461 can provide an output signal 473 as one or morenulls at the band 1; and the second nulling portion 481 can provide anoutput signal 493 as one or more nulls at the second band.

According to some embodiments, the nulling portions of respectivedifferent antenna array portions of the RF communication system 400 canprovide output signals as one or more nulls at a same band to abeamforming circuit as inputs. For example, the nulling portion 411 ofthe antenna array portion 402 can provide the output signal 423 as oneor more nulls at the band 1 to the beamforming circuit 454, and thenulling portion 461 of the antenna array portion 452 can provide theoutput signal 473 as one or more nulls at the band 1 to the beamformingcircuit 454. The nulling portion 431 of the antenna array portion 402can provide the output signal 445 as one or more nulls at the band 2 tothe beamforming circuit 456, and the nulling portion 481 of the antennaarray portion 452 can provide the output signal 493 as one or more nullsat the band 2 to the beamforming circuit 456.

Although two antenna array portions are shown in the illustratedembodiment of FIG. 4, the RF communication system 400 can include anydesired number of antenna array portions while remaining within thescope of the present disclosure. Although two nulling portions are shownin each of the antenna array portions of the RF communication system400, the RF communication system 400 can include any desired number ofnulling portions in each of the antenna array portions while remainingwithin the scope of the present disclosure. For example, the RFcommunication system 400 can include more than 2 antenna array portions,and/or each of the antenna array portions can include more than 2nulling portions.

In response to receiving the nulls at a certain band from the respectivenulling portions of different antenna array portions, the beamformingcircuit of the RF communication system 400 can use one or morebeamforming techniques (e.g., digital beamforming techniques, analogbeamforming techniques, hybrid beamforming techniques, and/or adaptivebeamforming techniques) to further minimize the nulls and/or generateone or more additional nulls. In some embodiments, such additional nullsmay be each pointed along a direction different from ones of the nullsprovided by the nulling portions. Such beamforming techniques may beknown in the art, so that the beamforming circuits 454 and 456 shall bebriefly discussed as follows. In some embodiments, the beamformingcircuit 454 may combine the output signals 423 and 473 to generatesignal 494 at band 1 in a way (e.g., respective different weights) wherean expected pattern or radiation is preferentially observed; and thebeamforming circuit 454 may combine the output signals 445 and 493 togenerate signal 495 at band 2 in a way (e.g., respective differentweights) where an expected pattern or radiation is preferentiallyobserved.

In response to the beamforming circuits 454 and 456 generating thesignals, respectively, in some embodiments, the combiner 458 can combinethe signals 494 and 495, and provide a single combined signal 496 to theRF front end 460 for further processing, as discussed above. Continuingwith the above example, the combiner 458 can combine (e.g., add) theoutput signals 494 and 495, each of which can include one or more nullsat the respective band, and provide the signal 496 to the RF front end460 for further processing.

Referring to FIGS. 5A-B, a functional block diagram of the RFcommunication system 500 is depicted. In some embodiments, the RFcommunication system 500 may selectively switch between a receiving modeand transmitting mode, which shall be discussed below. As shown in theillustrated embodiment of FIGS. 5A-B, the RF communication system 500can include a first RF head 502, a second RF head 542, a digitalprocessing subsystem 578, a digital-to-RF subsystem 584, and an RF frontend 594.

In some embodiments, the RF heads 502 and 542, each of which includes apair of antennas and components that can perform the above-describednulling function, can receive an RF signal to generate one or moredigital signals. Such one or more digital signals can include one ormore nulls, generated by performing the nulling function. The RFcommunication system 500 can use the one or more nulls to eliminate orminimize interferences that can be included in the received RF signals.The digital processing subsystem 578 can digitally process (e.g.,channelize, beamforming, etc.) the digital signals. The digital-to-RFsubsystem 584 can convert the digitally processed signal back to one ormore RF (e.g., analog) signals, and provide the one or more RF signalsto the RF front end 594 for further processing.

As shown in the illustrated embodiment of FIGS. 5A-B, the RF head 502can include a first antenna 504, a second antenna 506 separated from thefirst antenna 504 by a distance 505, a transmitting/receiving (T/R)switch 508, a bypass switch 510, filters (e.g., band-pass filters) 512and 514, time delay units (TDUs) 516 and 518, a subtractor 520, acontrol circuit 522, band-pass filters 524 and 528 with an amplifier 526coupled therebetween, an amplifier 530, and an analog-to-digitalconverter 532. The RF head 542 can include a first antenna 544, a secondantenna 546 separated from the first antenna 544 by a distance 545, atransmitting/receiving (T/R) switch 548, a bypass switch 550, filters(e.g., band-pass filters) 552, 554, and 556, time delay units (TDUs) 558and 560, a subtractor 562, a control circuit 564, band-pass filters 566and 570 with an amplifier 568 coupled therebetween, an amplifier 572,and an analog-to-digital converter 574. In some embodiments, the firstand second RF heads 502 and 542 can be substantially similar to eachother. Thus, the first RF head 502 is selected as a representativeexample in the following discussions.

The filters 512 and 514, TDUs 516 and 518, subtractor 520, and controlcircuit 522 are substantially similar to the components discussed ofFIG. 1A-4, respectively, such that the discussions are not repeated. Insome embodiments, the T/R switch 508 may switch the RF head 502 betweenthe receiving mode and transmitting mode based on a control signal. Forexample, when the control signal causes the T/R switch 508 to switch theRF head 502 to the receiving mode, the T/R switch 508 may allow a signalreceived by the antenna 504 to be received by the following subsystemsor circuits such as, for example, the RF front end 580. When the controlsignal causes the T/R switch 508 to switch the RF head 502 to thetransmitting mode, the T/R switch 508 may allow a signal directlyreceived from the RF front end 580 to be transmitted by the antenna 508.

In some embodiments, the bypass switch 510 can allow the signal receivedby the antenna 508 to bypass the following components of the RF head502, the digital processing subsystem 544, and a portion of thedigital-to-RF subsystem 550, and to be directly received by the RF frontend 580. In some embodiments, the bypass switch 510 may be controlled bya control signal to determine whether to allow the signal received bythe antenna 508 to bypass the following components of the RF head 502and the rest, as discussed above. In some embodiments, in response toallowing the bypass, the RF head 502 may not perform a nulling functionon the signal received by the antenna 508.

In response to the bypass not being allowed, the filters 512 and 514,TDUs 516 and 518, subtractor 520, and control circuit 522 can perform anulling function on the signals received by the antennas 506 and 508 togenerate an output signal 523, which may or may not include a null. Thecomponents 524-532 can “filter” and “sample” the signal 523, as known inthe art, such that the components 524-532 may be briefly described asfollows. In some embodiments, each of the filters 524 and 528 mayinclude a band-pass filter, wherein the filer 524 can allow a signalwith a very high frequency to pass and the filter 528 can reject imageand/or be anti-aliasing. The amplifier 526 may include a non-linearamplifier configured to avoid saturation. The amplifier 530 can avoidclipping. The analog-to-digital converter 532, which can receive a clocksignal, can convert the signal 523, through the respective operations ofthe components 524-530, into a digital signal 533. Similarly, the RFhead 542 can provide a digital signal 575 by using the includedcomponents to perform respective functions.

In some embodiments, the digital processing subsystem 578 can include afirst channelization circuit 579, a second channelization circuit 580, abeamforming circuit 581, and a mixer 582. The first channelizationcircuit 579 can channelize the digital signal 533, received from thefirst RF head 502, into a number of different (frequency) channels. Thesecond channelization circuit 580 can channelize the digital signal 575,received from the second RF head 542, into a number of different(frequency) channels. The beamforming circuit 581 can use at least oneof the above-mentioned beamforming techniques to process the signals ateach of the channels. The mixer 582 can then mix (e.g., convert) thesignals at different channels to a single processed signal 583.

The digital-to-RF subsystem 584 can include a digital-to-analogconverter 585, a mixer 586, a filter 587, an amplifier 588, a firstbypass filter 589, a second bypass filter 590, a first T/R switch 591,and a second T/R switch 582. The digital-to-analog converter 585 canconvert the signal 583 in the digital domain into the analog domain, andsuch a converted analog signal can be further processed by the mixer586, filter 587, and amplifier 588. The bypass switch 589 may becontrolled by the same control signal that controls the bypass switch510 of the RF head 502, and the bypass switch 590 may be controlled bythe same control signal that controls the bypass switch 550 of the RFhead 542. As such, when the bypass switch 510 allows the signal receivedby the antenna 508 to bypass the RF head 502, the digital processingsubsystem 578, and a portion of the digital-to-RF subsystem 584, thebypass switch 589 can route the signal to be directly received by the RFfront end 594 through the T/R switch 591. The bypass switch 590 and thebypass switch 550 of the RF head 542 may operate similarly.

The T/R switch 591 may be controlled by the same control signal thatcontrols the T/R switch 508 of the RF head 502, and the T/R switch 592may be controlled by the same control signal that controls the T/Rswitch 548 of the RF head 542. As such, when the T/R switch 508 switchswitches the RF head 502 to the receiving mode, the T/R switch 591 canallow the signal received from the bypass switch 589 to be received bythe RF front end 594. When the T/R switch 508 switch switches the RFhead 502 to the transmitting mode, the T/R switch 591 can allow thesignal received from the RF front end 594 to be transmitted through theantenna 504 directly. The T/R switch 592 and the T/R switch 548 of theRF head 542 may operate similarly.

B. Methods to Operate RF Communication Systems

FIG. 6 illustrates a flow chart of an exemplary method 600 to operate anRF communication system. In accordance with some embodiments of thepresent disclosure, the method 600 may be performed by the respectivecomponents of the RF communication systems 100, 130, and 160 discussedwith respect to FIGS. 1A-C. For purposes of discussion, the followingembodiment of the method 600 will be described in conjunction with FIGS.1A-D. The illustrated embodiment of the method 600 is merely an example.Therefore, it should be understood that any of a variety of operationsmay be omitted, re-sequenced, and/or added while remaining within thescope of the present disclosure.

In brief overview, a pair of antennas can receive an RF signal atoperation 602. At operation 604, one or more time delay units (TDUs) canmodify a time delay and/or power gain of at least one of receivedsignals. At operation 606, a subtractor can combine modified signals. Atoperation 608, a control circuit can determine whether the modifiedsignals are aligned. If not, the method 600 may proceed again tooperation 604; but if so, the method 600 proceeds to operation 610 inwhich the subtractor can generate a plurality of nulls. At operation612, the subtractor can provide an output signal, which can contain theplurality of nulls, to a receiver.

Referring still to FIG. 6, and in greater detail, the pair of antennascan receive an RF signal at operation 602. As a representative example,in FIG. 1A, the pair of antennas 102 and 104 can receive the RF signal116. In some embodiments, the pair of antennas 102 and 104 may bephysically separated apart from each other by distance 115. The distance115 can be associated with one or more characteristics of the RF signal116. For example, the distance 115 may be either greater or less than ahalf of the wavelength (λ/2) of the RF signal 116. As the separationdistance between the pair of antenna becomes larger than λ/2, one ormore aliased nulls can be generated by the RF communication system,which shall be discussed in further detail below with respect to FIG.10.

At operation 604, one or more time delay units (TDUs) can modify a timedelay and/or power gain of at least one of received signals. Accordingto some embodiments, in response to the pair of antennas receiving theRF signal, a first TDU, coupled to one of the pair of antennas, canmodify a corresponding signal received by the one of the pair ofantennas by applying a dynamically configurable time delay and/or powergain on the received signal. Simultaneously or subsequently, a secondTDU, coupled to the other of the pair of antennas, can modify acorresponding signal received by the other of the pair of antennas byapplying another dynamically configurable time delay and/or power gainon the received signal. In another embodiment, a phase shifter and/ortransmission line, coupled to the other of the pair of antennas, canmodify the signal received by the other of the pair of antennas byapplying a fixed time delay and/or power gain on the received signal.

Continuing with the example of FIG. 1A, the TDUs 106 and 108 can applydynamically configurable time delays and/or power gains on the signals118 and 120 that are respectively received by the antennas 102 and 104.In the example of FIG. 1B, one TDU 136 can apply a dynamicallyconfigurable time delay and/or power gain on the signal 150 that isreceived by the antenna 134, while the signal 148, received by theantenna 132, may be applied with no time delay or power gain.

At operation 606, the subtractor combines the modified signals.According to some embodiments, in response to the received signals beingmodified, the subtractor, coupled to the TDU(s), combines (e.g.,subtract) the modified signals to generate an output signal.

At operation 608, the control circuit can determine whether the modifiedsignals are aligned. According to some embodiments, in response to thesubtractor combining the modified signals, the control circuit candetermine whether the modified signals are aligned in time and powerlevels by monitoring or detecting whether a power level of the outputsignal has reach a minimum. In some embodiments, the control circuit caniteratively adjust the time delay(s) and/or power gain(s) that theTDU(s) apply on the respective received signal(s) until the controlcircuit has detected a minimum of the power levels of the output signalover a number of iterations.

If the control circuit cannot determine a minimum of the power level ata current iteration, the control circuit can update the time delay(s)and/or power gain(s) that the TDU(s) apply on the received signal(s)(operation 604). If the control circuit can determine a minimum of thepower level at the current iteration, the subtractor can provide theoutput signal, generated by combining the modified signals, as aplurality of nulls (operation 610). In some embodiments, in response tothe control circuit determining the minimum power level of the outputsignal, the control circuit can record, manage, or store the timedelay(s) and/or power gain(s) that the TDU(s) apply on the receivedsignal(s).

At operation 612, the subtractor can provide the output signal, whichcan contain the plurality of nulls, to the receiver. In the case wherethe receiver receives an output signal containing nulls, the receivermay receive an RF signal through the antennas that is aligned withrespective directions of the nulls. In some embodiments, the subtractormay provide an output signal to the receiver, which can be an RF frontend, during each time of the iterations. As the control circuit caniteratively update the time delay(s) and/or power gain(s) that theTDU(s) apply on the received signal(s), at least one of the outputsignals respectively provided over the plural iterations can include anull. The RF front end can use such a null to eliminate or minimize aknown or an unknown interference.

FIG. 7 illustrates a flow chart of an exemplary method 700 to operate anRF communication system. In accordance with some embodiments of thepresent disclosure, the method 700 may be performed by the respectivecomponents of the RF communication system 200 discussed with respect toFIG. 2. For purposes of discussion, the following embodiment of themethod 700 will be described in conjunction with FIG. 2. The illustratedembodiment of the method 700 is merely an example. Therefore, it shouldbe understood that any of a variety of operations may be omitted,re-sequenced, and/or added while remaining within the scope of thepresent disclosure.

In brief overview, multiple pairs of antennas can receive an RF signalat operation 702. At operation 704, one or more filters, coupled to arespective pair of antennas, may filter received signals. At operation706, one or more time delay units (TDUs), coupled to the respective pairof antennas, can modify a time delay and/or power gain of at least oneof the filtered signals. At operation 708, a subtractor, coupled to therespective pair of antennas, can combine modified signals. At operation710, a control circuit, coupled to the respective pair of antennas, candetermine whether the modified signals are aligned. If not, the method700 may proceed again to operation 706; but if so, the method 700proceeds to operation 712 in which the subtractor can generate aplurality of (spatial) nulls at a respective band. At operation 714, acombiner can combine output signals from respective subtractors. Atoperation 716, the combiner can provide a combined signal, which cancontain the plurality of nulls at respective bands, to a receiver.

Referring still to FIG. 7, and in greater detail, the multiple pairs ofantennas can receive the RF signal at operation 702. Using the RFcommunication system 200 of FIG. 2 as an example, the pair of antennas212 and 214 and the pair of antennas 232 and 234 can respectivelyreceive the RF signal 254. The pair of antennas 212 and 214 may bephysically separated apart from each other by distance 227; and the pairof antennas 232 and 234 may be physically separated apart from eachother by distance 247. The distances 227 and 247 can be each associatedwith one or more characteristics (e.g., a wavelength) of the RF signal254. In some embodiments, the antennas 212 and 214 may be referred to asa part of the antenna portion 210; and the antennas 232 and 234 may bereferred to as a part of the antenna portion 230.

At operation 704, the one or more filters, coupled to the respectivepair of antennas, may filter the received signals. In response toreceiving the RF signal, the one or more filters may each use arespective frequency range (or band) to allow a portion of the signalreceived by the respective pair of antennas to pass therethrough. Theone or more filters can be referred to as frequency filters. Continuingwith the example of FIG. 2, the filters 216 and 218, respectivelycoupled to the antennas 212 and 214, can filter the signals respectivelyreceived by the antennas 212 and 214; and the filters 236 and 238,respectively coupled to the antennas 232 and 234, can filter the signalsrespectively received by the antennas 232 and 234. In some embodiments,the filters 216 and 218 may filter out the portions of the receivedsignals (e.g., 256 and 258) that are outside the band 1, and leave theportions of the received signals that are within the band 1; and filters236 and 238 may filter out the portions of the received signals that areoutside the band 2, and leave the portions of the received signals thatare within the band 2. In some embodiments, the bands 1 and 2 may bereferred to respective different frequency ranges.

At operation 706, the one or more time delay units (TDUs), coupled tothe respective pair of antennas, can modify the time delay and/or powergain of at least one of the filtered signals. In response to the one ormore filters filtering the respective received signals, one or more TDUscan modify the filtered signals by applying dynamically configurabletime delays and/or power gains on the filtered signals. Using theexample of FIG. 2 again, the TDUs 220 and 222 can apply dynamicallyconfigurable time delays and/or power gains on the signals that arerespectively filtered (e.g., allowed to pass) by the filters 216 and218; and the TDUs 240 and 242 can apply dynamically configurable timedelays and/or power gains on the signals that are respectively filtered(e.g., allowed to pass) by the filters 236 and 238.

At operation 708, the subtractor, coupled to the respective pair ofantennas, can combine modified signals. In response to the one or moreTDUs modifying the received signals, the subtractor can combine (e.g.,subtract) the modified signals to generate an output signal. Using theexample of FIG. 2 again, the subtractor 226 can combine (e.g., subtract)the signals respectively modified by the TDUs 220 and 222 to generate anoutput signal; and the subtractor 246 can combine (e.g., subtract) thesignals respectively modified by the TDUs 240 and 242 to generate anoutput signal.

At operation 710, the control circuit, coupled to the respective pair ofantennas, can determine whether the modified signals are aligned. Inresponse to the generation of the output signal, the control circuit candetermine whether the modified signals are aligned in time and powerlevels by monitoring or detecting whether a power level of the outputsignal has reach a minimum. In some embodiments, the control circuit caniteratively adjust the time delays and/or power gains that the one ormore TDUs apply on the respective filtered signals until the controlcircuit has detected a minimum of the power levels of the output signalover a number of iterations.

Continuing with the example of FIG. 2, the control circuit 224 caniteratively adjust the time delays and/or power gains that the TDUs 220and 222 apply on the respective signals, filtered by the filters 216 and218, until the control circuit 224 has detected a minimum of the powerlevels of the output signal 264 over a number of iterations; and thecontrol circuit 244 can iteratively adjust the time delays and/or powergains that the TDUs 240 and 242 apply on the respective signals,filtered by the filters 236 and 238, until the control circuit 244 hasdetected a minimum of the power levels of the output signal 266 over anumber of iterations.

If the control circuit cannot determine a minimum of the power level ata current iteration, the control circuit can update the time delay(s)and/or power gain(s) that the one or more TDUs apply on the filteredsignals (operation 706). If the control circuit can determine a minimumof the power level at the current iteration, the subtractor can providethe output signal, generated by combining the modified signals, as aplurality of nulls at the respective band (operation 712).

At operation 714, the combiner can combine the output signals from therespective subtractors. Using the above example again, the combiner 250can combine the output signals 264 and 266 provided by the subtractors226 and 246, respectively. At operation 716, the combiner can providethe one or more nulls at respective bands to the receiver. Continuingwith the example of FIG. 2, the combiner 250 may provide the outputsignal 268 to the receiver, which can be an RF front end 252, duringeach time of the iterations. As the control circuits 224 and 244 caniteratively update the time delays and/or power gains that the TDUsapply on the filtered signals, the output signals 264 and 266respectively provided over the plural iterations can include a pluralityof nulls at respective bands. In other words, a first plurality of nullsat a first band can be included in the output signal 264; and a secondplurality of nulls at a second band can be included in the output signal266. Upon receiving the output signals 264 and 266, the RF front end canuse such nulls, included in the output signals 264 and 266, to eliminateor minimize known or unknown interferences at respective bands.

FIG. 8 illustrates a flow chart of an exemplary method 800 to operate anRF communication system. In accordance with some embodiments of thepresent disclosure, the method 800 may be performed by the respectivecomponents of the RF communication system 300 discussed with respect toFIG. 3. For purposes of discussion, the following embodiment of themethod 800 will be described in conjunction with FIG. 3. The illustratedembodiment of the method 800 is merely an example. Therefore, it shouldbe understood that any of a variety of operations may be omitted,re-sequenced, and/or added while remaining within the scope of thepresent disclosure.

In brief overview, a pair of antennas can receive an RF signal atoperation 802. At operation 804, a pair of splitters can route receivedsignals. At operation 806, one or more filters can filter respectiverouted signals. At operation 808, one or more time delay units (TDUs)can modify a time delay and/or power gain of at least one of thefiltered signals. At operation 810, a subtractor, coupled to respectivefilters, can combine modified signals. At operation 812, a controlcircuit, coupled to the respective filters, can determine whether themodified signals are aligned. If not, the method 800 may proceed againto operation 808; but if so, the method 800 proceeds to operation 814 inwhich the subtractor can generate a plurality of nulls at a respectiveband. At operation 816, a combiner can combine output signals fromrespective subtractors. At operation 818, the combiner can provide acombined signal, which can contain the plurality of nulls at respectivebands, to a receiver.

Referring still to FIG. 8, and in greater detail, the pair of antennascan receive an RF signal at operation 802. Using the RF communicationsystem 300 of FIG. 3 as an example, the pair of antennas 302 and 304 canrespectively receive the RF signal 350. The pair of antennas 302 and 304may be physically separated apart from each other by distance 303. Thedistance 303 can be each associated with one or more characteristics(e.g., a wavelength) of the RF signal 350.

At operation 804, the pair of splitters can route received signals.Using the above example of FIG. 3 again, the splitter 306 can route thesignal 352 received by the antenna 302 by dividing the signal 352 intorouted signals 352-1 and 352-2 and forward the signals 352-1 and 352-2to the nulling portions 310 and 330, respectively; and the splitter 308can route the signal 354 received by the antenna 304 by dividing thesignal 354 into routed signals 354-1 and 354-2 and forward the signals354-1 and 354-2 to the nulling portions 310 and 330, respectively.

At operation 806, the one or more filters can filter the respectiverouted signals. In response to receiving the routed signal, the one ormore filters at each nulling portion may each use a respective frequencyrange (or band) to allow a portion of the routed signal to passtherethrough. Continuing with the example of FIG. 3, the filters 312 and314 at the nulling portion 310 can filter the signals respectivelyrouted by the splitters 306 and 308; and the filters 332 and 334 at thenulling portion 330 can filter the signals respectively routed by thesplitters 306 and 308. In some embodiments, the filters 312 and 314 mayfilter out the portions of the routed signals (e.g., 352-1 and 354-1)that are outside the band 1, and leave the portions of the routedsignals that are within the band 1; and filters 332 and 334 may filterout the portions of the routed signals (e.g., 652-2 and 354-2) that areoutside the band 2, and leave the portions of the received signals thatare within the band 2. In some embodiments, the bands 1 and 2 may bereferred to respective different frequency ranges.

At operation 808, the one or more time delay units (TDUs) can modify thetime delay and/or power gain of at least one of the filtered signals. Inresponse to the one or more filters filtering the respective receivedsignals, one or more TDUs can modify the filtered signals by applyingdynamically configurable time delays and/or power gains on the filteredsignals. Using the example of FIG. 3 again, the TDUs 316 and 318 canapply dynamically configurable time delays and/or power gains on thesignals that are respectively filtered (e.g., allowed to pass) by thefilters 310 and 314; and the TDUs 336 and 338 can apply dynamicallyconfigurable time delays and/or power gains on the signals that arerespectively filtered (e.g., allowed to pass) by the filters 332 and334.

At operation 810, the subtractor, coupled to the respective filters, cancombine modified signals. In response to the one or more TDUs modifyingthe received signals, the subtractor can combine (e.g., subtract) themodified signals to generate an output signal. Using the example of FIG.3 again, the subtractor 322 can combine (e.g., subtract) the signalsrespectively modified by the TDUs 316 and 318 to generate an outputsignal; and the subtractor 342 can combine (e.g., subtract) the signalsrespectively modified by the TDUs 336 and 338 to generate an outputsignal.

At operation 812, the control circuit, coupled to the respectivefilters, can determine whether the modified signals are aligned. Inresponse to the generation of the output signal, the control circuit candetermine whether the modified signals are aligned in time and powerlevels by monitoring or detecting whether a power level of the outputsignal has reach a minimum. In some embodiments, the control circuit caniteratively adjust the time delays and/or power gains that the one ormore TDUs apply on the respective filtered signals until the controlcircuit has detected a minimum of the power levels of the output signalover a number of iterations.

Continuing with the example of FIG. 3, the control circuit 320 caniteratively adjust the time delays and/or power gains that the TDUs 316and 318 apply on the respective signals, filtered by the filters 312 and314, until the control circuit 320 has detected a minimum of the powerlevels of the output signal 356 over a number of iterations; and thecontrol circuit 340 can iteratively adjust the time delays and/or powergains that the TDUs 336 and 338 apply on the respective signals,filtered by the filters 332 and 334, until the control circuit 340 hasdetected a minimum of the power levels of the output signal 266 over anumber of iterations.

If the control circuit cannot determine a minimum of the power level ata current iteration, the control circuit can update the time delay(s)and/or power gain(s) that the one or more TDUs apply on the filteredsignals (operation 808). If the control circuit can determine a minimumof the power level at the current iteration, the subtractor can providethe output signal, generated by combining the modified signals, as aplurality of nulls at the respective band (operation 814).

At operation 816, the combiner can combine the output signals from therespective subtractors. Using the above example again, the combiner 344can combine the output signals 356 and 358 provided by the subtractors322 and 342, respectively. At operation 818, the combiner can providethe plurality of nulls at respective bands to the receiver. Continuingwith the example of FIG. 3, the combiner 344 may provide the outputsignal 360 to the receiver, which can be an RF front end 346, duringeach time of the iterations. As the control circuits 320 and 340 caniteratively update the time delays and/or power gains that the TDUsapply on the filtered signals, at least one of the output signals 356and 358 respectively provided over the plural iterations can include anull at a respective band. The RF front end can use such a null toeliminate or minimize a known or an unknown interference.

C. Nulls Generated by RF Communication Systems

Referring to FIGS. 9A and 9B, a symbolic diagram 900 of exemplary nullsand a corresponding antenna polar plot 920 of the exemplary nulls aredepicted, respectively. As shown in the illustrated embodiment of FIG.9A, a pair of antennas 902 and 904 can be arranged along an axis 905.The pair of antennas 902 and 904 can be a part of one of theabove-discussed RF communication systems (e.g., 100, 130, 160, 200, 300,400, and 500) that are configured to receive one or more RF signals. Insome embodiments, each of the antennas 902 and 904 can be anomnidirectional antenna.

By performing the nulling function discussed above, a null 910, and anull 912 symmetrically mirrored from the null 910 over the axis 905 canbe both generated, in accordance with some embodiments of the presentdisclosure. For example, the null 910 can be tilted from an axis 907,substantially perpendicular to the axis 905, by an angle θ, while thenull 912 can be tilted from the axis 907 by the same angle θ. In someembodiments, the null 912 can be referred to as a symmetric orsympathetic null with respect to the null 910.

Referring to FIG. 9B, the antenna polar plot 920, corresponding to thesymbolic diagram 900 of FIG. 9A, is illustrated. As shown in FIG. 9B,the respective power levels (in the unit of dB) of null 910 and symbolicnull 912 can each present a minimum on the antenna polar plot 920, andeach of the minimum power levels can be aligned along a certaindirection with respect to the antennas 902 and 904. As discussed above,each of the disclosed RF communication systems can utilize the nulls toeliminate or minimize interferences, for example, adjusting thedirection along which the null is aligned to be aligned with a source ofthe interference.

In some embodiments, the spacing (e.g., 115, 135, 177, 227, 247, 303,505, and 545) between a pair of antennas of the disclosed RFcommunication system can be adjusted to be greater than a half of thewavelength of the RF signal received by the antennas. As such, one ormore aliased nulls, as mentioned above, can be generated by thedisclosed RF communication systems.

FIG. 10 illustrates a number of exemplary symbolic diagrams of nullsand/or aliased nulls with respect to a pair of antennas 1001A and 1001B,and corresponding antenna polar plots. In some embodiments, the antennas1001A and 1001B may be separated from each other by a fixed distance.The distance can be associated with the wavelength of the RF signalreceived by the antenna 1001A and 1001B (e.g., quantized by thewavelength). When the frequency of the RF signal (reciprocal to thewavelength) varies, quantized weights of the distance may vary. When thequantized weight of the distance becomes greater than ½ (i.e., thedistance between antennas 1001A and 1001B, when expressed in wavelength,is greater than ½ wavelength), in some embodiments, the one or morealiased nulls can be generated by the disclosed RF communicationsystems. In some embodiments, the disclosed RF communication system canperform the nulling function to adjust the time delays that therespective TDUs use, thereby causing a certain range of time delays toinclude more RF cycles. In response to including more RF cycles, the RFcommunication system can generate more aliased nulls accordingly.

For example, when the frequency of the RF signal is about 2 GHz, a pairof nulls 1003A and 1003B can be generated by a currently disclosed RFcommunication system that includes the antennas 1001A and 1001B, whichcan be seen in the symbolic diagram 1002 and corresponding antenna polarplot 1004. As the frequency of the RF signal becomes about 3 GHz, a pairof aliased nulls 1007A and 1007B can be generated, which can be seen inthe symbolic diagram 1006 and corresponding antenna polar plot 1008. Asthe frequency of the RF signal becomes about 4 GHz, a pair of aliasednulls 1011A and 1011B (along with different directions than the aliasednulls 1007A-B) can be generated, which can be seen in the symbolicdiagram 1010 and corresponding antenna polar plot 1012. As the frequencyof the RF signal becomes about 5 GHz, two pairs of aliased nulls 1015Aand 1015B and 1015C and 1015D can be generated, which can be seen in thesymbolic diagram 1014 and corresponding antenna polar plot 1016. As thefrequency of the RF signal becomes about 6 GHz, two pairs of aliasednulls 1019A and 1019B and 1019C and 1019D can be generated, which can beseen in the symbolic diagram 1018 and corresponding antenna polar plot1020.

FIGS. 11A and 11B respectively illustrates examples in which thedirections of nulls generated with respect to two different pairs ofantennas can be adjusted, in accordance with some embodiments of thepresent disclosure. Referring first to FIG. 11A, an RF communicationsystem 1100 can include a first pair of antennas 1104A-B and a secondpair of antennas 1114A-1114B. The RF communication system 1100 can bedeployed on a device (e.g., a vehicle), which may move along a direction1101 in the illustrated embodiment of FIG. 11A. On or in the device, thefirst pair of antennas 1102A-B can be deployed along an axis 1103, andthe second pair of antennas 1112A-B can be deployed along an axis 1113.The axis 1103 can be aligned along a direction either different from orsimilar to the direction along which the axis 1113 extends.

By performing the above-discussed nulling function, the RF communicationsystem 1100 can generate a pair of nulls 1104A-B with respect to theantennas 1102A-B, and a pair of nulls 1114A-B with respect to theantennas 1112A-B. In a case where an interference source 1120 is locatedalong the direction 1101, the RF communication system can align oroverlap the directions of null 1104A and 1114A to eliminate or minimizethe interference by performing the nulling function and/or adjusting thedirections of axis 1103 and axis 1113.

FIG. 11B illustrates another example in which an interference source1122 is located away from the direction 1101. To eliminate or minimizethe interference, the RF communication system 1100 can generate anotherpair of nulls 1124A-B with respect to the antennas 1102A-B by performingthe nulling function and/or adjusting the direction of axis 1103, andanother pair of nulls 1134A-B with respect to the antennas 1112A-B byperforming the nulling function and/or adjusting the direction of axis1113. As such, at least two of the nulls (e.g., 1124A and 1134A in FIG.11B) can be combined to be aligned with the interference source 1122,even though no nulls are overlapped.

The construction and arrangement of the systems and methods as shown inthe various exemplary embodiments are illustrative only. Although only afew embodiments have been described in detail in this disclosure, manymodifications are possible (e.g., variations in sizes, dimensions,structures, shapes and proportions of the various elements, values ofparameters, mounting arrangements, use of materials, colors,orientations). For example, the position of elements may be reversed orotherwise varied and the nature or number of discrete elements orpositions may be altered or varied. Accordingly, all such modificationsare intended to be included within the scope of the inventive conceptsdisclosed herein. The order or sequence of any operational flow ormethod operations may be varied or re-sequenced according to alternativeembodiments. Other substitutions, modifications, changes, and omissionsmay be made in the design, operating conditions and arrangement of theexemplary embodiments without departing from the broad scope of theinventive concepts disclosed herein.

The inventive concepts disclosed herein contemplate methods, systems andprogram products on any machine-readable media for accomplishing variousoperations. Embodiments of the inventive concepts disclosed herein maybe implemented using existing computer operational flows, or by aspecial purpose computer operational flows for an appropriate system,incorporated for this or another purpose, or by a hardwired system.Embodiments within the scope of the inventive concepts disclosed hereininclude program products comprising machine-readable media for carryingor having machine-executable instructions or data structures storedthereon. Such machine-readable media can be any available media that canbe accessed by a special purpose computer or other machine with anoperational flow. By way of example, such machine-readable media cancomprise RAM, ROM, EPROM, EEPROM, CD-ROM or other optical disk storage,magnetic disk storage or other magnetic storage devices, or any othermedium which can be used to carry or store desired program code in theform of machine-executable instructions or data structures and which canbe accessed by a general purpose or special purpose computer or othermachine with an operational flow. When information is transferred orprovided over a network or another communications connection (eitherhardwired, wireless, or a combination of hardwired or wireless) to amachine, the machine properly views the connection as a machine-readablemedium. Thus, any such connection is properly termed a machine-readablemedium. Combinations of the above are also included within the scope ofmachine-readable media. Machine-executable instructions include, forexample, instructions and data which cause a special purpose computer,or special purpose operational flowing machines to perform a certainfunction or group of functions.

What is claimed is:
 1. A system for cancelling interference, the systemcomprising: a first antenna; a second antenna spatially separated fromthe first antenna; a first time delay unit, coupled to the firstantenna, and configured to apply a first time delay and first power gainon a first signal received by the first antenna to provide a modifiedversion of the first signal; a third antenna; a fourth antenna spatiallyseparated from the third antenna; a second time delay unit, coupled tothe third antenna, and configured to apply a second time delay andsecond power gain on a second signal received by the third antenna toprovide a modified version of the second signal; a processor, coupled tothe first time delay unit, and configured to determine the first timedelay and first power gain to cause the modified version of the firstsignal and a third signal received by the second antenna to be alignedin time and power level, wherein the processor is further coupled to thesecond time delay unit and is configured to determine the second timedelay and second power gain to cause the modified version of the secondsignal and a fourth signal received by the fourth antenna to be alignedin time and a power level; a first subtractor configured to subtractrespective power levels of the modified version of the first signal andthe third signal to provide a first output signal, wherein the firstoutput signal provides at least a first null; and a second subtractorconfigured to subtract respective power levels of the modified versionof the second signal and the fourth signal to provide a second outputsignal, wherein the second output signal provides at least a secondnull, and wherein the first null and the second null are symmetricallymirrored by an axis connecting the first and second antennas.
 2. Thesystem of claim 1, wherein the processor is coupled to the first andsecond subtractor and is configured to use the first and second outputsignal to determine the first time delay and first power gain and thesecond time delay and second gain, respectively.
 3. The system of claim1, further comprising: a first frequency filter coupled between thefirst antenna and first time delay unit; and a second frequency filtercoupled between the third antenna and second time delay unit, whereinthe first and second frequency filters are configured to allow a signalwithin a first frequency range to pass therethrough.
 4. The system ofclaim 1, further comprising: a mutual coupling mitigation circuit,coupled between the first and second antennas and the first time delayunit, and configured to substantially reduce a power level of aninterference signal received by one of the first and second antennas andre-radiated from the other of the first and second antennas.
 5. A systemfor automatically cancelling interference, the system comprising: afirst antenna; a second antenna spatially separated from the firstantenna; a first time delay unit configured to apply a first time delayand first power gain on a first signal received by the first antenna toprovide a modified version of the first signal; a third antenna; afourth antenna spatially separated from the third antenna; a second timedelay unit configured to apply a second time delay and second power gainon a second signal received by the third antenna to provide a modifiedversion of the second signal; a first frequency filter coupled betweenthe first antenna and first time delay unit; a second frequency filtercoupled between the second antenna and second time delay unit, whereinthe first and second frequency filters are configured to allow a signalwithin a first frequency range to pass therethrough; a first combinerconfigured to combine the modified version of the first signal and athird signal provided from the second antenna; a second combinerconfigured to combine the modified version of the second signal and afourth signal provided from the fourth antenna; a third frequency filtercoupled between the second antenna and first combiner; a fourthfrequency filter coupled between the fourth antenna and second combiner,wherein the third and fourth frequency filters are configured to allow asignal within a second frequency range to pass therethrough; and acontrol circuit configured to determine the first and second time delaysand first and second power gains to cause the modified version of thefirst signal and the third signal to be aligned in time and power levelsand the modified version of the second signal and the fourth signal tobe aligned in time and power levels, wherein the control circuit isfurther configured to determine a power level of a first output signalreceived from the first combiner and a power level of a second outputsignal received from the second combiner, wherein the first outputsignal provides at least a first null and a second null and the secondoutput signal provides at least a third null and a fourth null, whereinthe first and second nulls are symmetrically mirrored by a first axisconnecting the first and second antennas, and wherein the third andfourth nulls are symmetrically mirrored by a second axis connecting thethird and fourth antennas.
 6. The system of claim 5, wherein the firstfrequency range is different from the second frequency range.
 7. Thesystem of claim 5, wherein at least one of the first or second nulls andat least one of the third or fourth nulls are aligned along a samedirection, or none of the first, second, third, or fourth nulls isaligned along a same direction.
 8. A system for automatically cancellinginterference, the system comprising: a first antenna; a second antennaspatially separated from the first antenna; a first time delay unitconfigured to apply a first time delay and first power gain on a firstsignal received by the first antenna to provide a first modified versionof the first signal; a second time delay unit configured to apply asecond time delay and second power gain on a second signal received bythe second antenna to provide a second modified version of the secondsignal; a third antenna; a fourth antenna spatially separated from thethird antenna; a third time delay unit configured to apply a third timedelay and third power gain on a third signal received by the thirdantenna to provide a third modified version of the third signal; afourth time delay unit configured to apply a fourth time delay andfourth power gain on a fourth signal received by the fourth antenna toprovide a fourth modified version of the fourth signal; a firstsubtractor configured to subtract respective power levels of the firstmodified version of the first signal and the second modified version ofthe second signal to provide a first output signal; a first controlcircuit configured to determine the first and second time delays andfirst and second power gains based on a power level of the first outputsignal to cause the first modified version of the first signal and thesecond modified version of the second signal to be aligned in time andpower levels; a second subtractor configured to subtract respectivepower levels of the third modified version of the third signal and thefourth modified version of the fourth signal to provide a second outputsignal; and a second control circuit configured to determine the thirdand fourth time delays and third and fourth power gains based on a powerlevel of the second output signal to cause the third modified version ofthe third signal and the fourth modified version of the fourth signal tobe aligned in time and power levels.
 9. The system of claim 8, furthercomprising: a first frequency filter configured to allow the firstsignal, routed by a first splitter, to pass therethrough to be receivedby the first time delay unit, responsive to the first signal beingwithin a first frequency range; a second frequency filter configured toallow the second signal, routed by a second splitter, to passtherethrough to be received by the second time delay unit, responsive tothe second signal being within the first frequency range; a thirdfrequency filter configured to allow the first signal, routed by thefirst splitter, to pass therethrough to be received by the third timedelay unit, responsive to the first signal being within a secondfrequency range; and a fourth frequency filter configured to allow thesecond signal, routed by the second splitter, to pass therethrough to bereceived by the fourth time delay unit, responsive to the second signalbeing within the second frequency range.
 10. The system of claim 9,wherein the first frequency range is different from the second frequencyrange.
 11. The system of claim 8, further comprising: a combinerconfigured to combine the first and second output signals to provide asingle output signal for a receiver.
 12. The system of claim 8, whereinthe first output signal provides at least a first null and a second nulland the second output signal provides at least a third null and a fourthnull, the first and second nulls being symmetrically mirrored by an axisconnecting the first and second antennas and third and fourth nullsbeing symmetrically mirrored by the axis connecting the first and secondantennas.
 13. The system of claim 12, wherein at least one of the firstor second nulls and at least one of the third or fourth nulls arealigned along a same direction, or none of the first, second, third, orfourth nulls is aligned along a same direction.